Scoliosis, defined as lateral curvature of the spinal column, has in its mildest form an impact on cosmetic appearance alone, while severe scoliosis signifies deformity and cardiopulmonary impairment, remedial only by corrective spinal surgery. Initially, electrical stimulation through implanted electrodes appeared to be a feasible alternative to bracing in the treatment of progressive scoliosis in the growing child or teen-ager.sup.1. FNT .sup.1 Bobechko, W. P., Herbert, M. A.: Results of Using Electro-Spinal Instrumentation for the Treatment of Scoliosis at the Hospital for Sick Children, Toronto. Interim Report. Neuro-Rehabilitation Division, Medtronic, Inc., Oct. 1975.
Thereafter, this applicant has developed a clinical program for the treatment of idiopathic scoliosis using Lateral Electrical Surface Stimulation (LESS).sup.2,3,4,5. This included the design and production of a portable patient stimulator and the use of an appropriate surface electrode system. FNT .sup.2 Rehabilitation Engineering Center at Rancho Los Amigos Hospital, Annual Report of Progress, 1976, pp. 12-14. FNT .sup.3 Axelgaard, J.: Scoliotic Curvature Induced by Electrical Stimulation. Final Project Report, Rehabilitation Engineering Center, Rancho Los Amigos Hospital, August, 1976. FNT .sup.4 Rehabilitation Engineering Center at Rancho Los Amigos Hospital, Annual Report of Progress, 1977, pp. 12-15. FNT .sup.5 Rehabilitation Engineering Center at Rancho Los Amigos Hospital, Annual Report of Progress, 1978, pp. 13-16. semi-solid conductive media (Ceptorpad.TM.) or coated with electrolytic gel (Spectra 360.TM.) for a low impedance electrode-skin interfacing. Two of such electrodes were placed on the skin on the convex side of the curvature, symmetrically around the apex, in a medial (1) and two lateral locations [(2) intermediate, (3) full lateral] across the back (FIG. 1). A constant-current battery-operated generator supplied square wave pulses of 0.2 msec duration, 70 mA in amplitude, and at a rate of 30 pps. Duration of the wave pulses, amplitude and rate were all adjustable as set forth in the said pending application Ser. No. 50,760.
The ESS-screening results, from a number of idopathic patients, proved that lateral electrode placement was the most effective configuration in acute curvature correction. On the average, the major stimulated curve corrected 2 degrees in the medial configuration* (3 cm lateral to the spinous processes), while the non-stimulated compensatory curve became 2 degrees worse. In the intermediate location, (2; FIG. 1, halfway between medial and lateral), the major curve improved 7 degrees and the minor curve improved 3 degrees. The lateral configuration (3; FIG. 1, electrodes on axillary line) exhibited 8 degrees of correction for the major stimulated curve while the compensatory curve corrected 4 degrees. FNT *FIG. 1,1
Based on the results of such ESS-screening, Lateral Electrical Surface Stimulation (LESS) appears to be the treatment of choice of the treatment of progressive scoliosis and other spinal curvature deficiencies.
In the preferred method of treatment, as set forth in detail in said patent application Ser. No. 50,760, LESS is applied during the hours of sleep only, with an ON/OFF ratio of, for example 2:1 to 1:4 with OFF being five seconds or larger to prevent muscle fatigue. The LESS treatment follows that set forth, generally, above, i.e. the stimulating electrodes are placed symmetrically, about the reference center or apex of the major curvature to be reduced (in the thoracic area, the electrodes are placed about the apical rib as detailed in said Ser. No. 50,760, and in general, along the axillary line of the lateral muscles of the patient). The stimulus pulses applied to the selected muscle site are preferably DC compensated monophasic, (i.e. a zero net charge flows between electrodes) and have an amplitude of between about 60-80 mAmp, about 100-40 sec pulse width and about 20-30 pps. The details of the electrode placement, and electrical stimulation are more particularly set forth in said pending application Ser. No. 50,760.
The main objective of LESS treatment is not principally to strengthen the muscles being stimulated, but to cause asymmetrical pressures to be exerted on growth zones so as to effect a biomechanical straightening of the spine. Specifically, by applying lateral electrical stimulation to the surface of the skin, proximate specific trunk muscles, rather significant mechanical forces can be applied to the spine.
The reason why lateral muscle stimulation provides the most effective corrective force can readily be explained biomechanically. The medial, paraspinal muscles comprise a large muscle mass capable of generating large contraction forces when stimulated electrically, but the forces are mainly directed in a longitudinal direction which have only little effect on scoliotic curves because of the smaller lever arm of these muscles. On the other hand, when the smaller muscle mass of the lateral muscles are electrically stimulated, forces are produced which act on the ribs or ribs and pelvis, and strong moments are created which exert powerful lateral corrective forces on the spine.
It would seem quite clear that scoliosis correction would become more efficient by applying a constant force on the convexity of the scoliosis curvature. This approach implies a constant muscular contraction of muscle groups on the convexity of the curve. However, if the same muscle group is constantly stimulated, it will quickly fatigue and lose its developed tension. The invention herein provides a method of imparting a constant corrective force on the curvature to be reduced without causing the onset of muscle fatigue.